Liquid crystal display devices (hereinafter, referred to as “LCDs”), which are representative flat panel display devices, include a lower TFT substrate to which transparent pixel electrodes are connected through switching units and an upper color filter substrate formed with common electrodes.
A liquid crystal having an anisotropic characteristic is provided between the substrates of such an LCD, and a backlight unit capable of irradiating light onto the whole area of a screen of the LCD with uniform brightness is required so as to allow pixels of the LCDs to emit light.
Although a cold cathode fluorescent lamp (CCFL) is mainly used as a backlight unit of an LCD, the cold cathode fluorescent lamp (CCFL), which is a side light source, requires elements such as a prism in order to spread light over the entire surface of the LCD. Accordingly, it is difficult to reduce the thickness and costs of the LCD.
For this reason, studies have been performed in relation to a surface light source which irradiates external light onto the entire screen of the LCD with uniform brightness. To this end, a backlight unit using a high-power and high-brightness light emitting diode (LED) has been developed.
In general, a LED package is provided to a side portion of a backlight unit, and light emitted from the LED package is incident onto an LCD positioned above a light guide plate through the light guide plate such that the LCD can serve as a display.
However, the LED of the backlight unit has a light efficiency of about 301 m/W, which is much lower than a light efficiency (about 851 m/W) of the cold cathode fluorescent lamp.
In general, the LED has a light efficiency corresponding to a half or less of a light efficiency of the cold cathode fluorescent lamp. In addition, since energy of the LED that is not used as a light source is converted into heat, a problem of heat generation may occur.
Due to the heat generation, the temperature of the LCD using the LED rises by 10° C. or more as compared with that of an LCD using the cold cathode fluorescent lamp when the LCD operates for a long time.
Accordingly, if heat of the LED is not discharged to an exterior, but continuously accumulated in the LCD, the LCD is deteriorated, so that display quality may be degraded, or colors of the LCD may be changed. In addition, the heat may degrade the endurance and the reliability of the LED.
Further, since a high-brightness and high-power LED is necessary, heat dissipation has been mainly issued as a problem in the LED package.
If the intensity of current increases to obtain high-power light from an LED package, heat having the high temperature may be generated from the LED. If the internal temperature of the LED package rises due to the generated heat, resistance may highly increase so that light efficiency is lowered.